The reality of climate change on our oceans
We may be aware that climate change is the largest and greatest threat to us as a species as well as the planet; yet it has only recently been accepted, prompting much-needed serious discussion around the subject. The original term global warming has thankfully been replaced by the more informative and correct term, climate change. This is because our climate isn’t simply warming; in fact, it is fluctuating on a global scale.
In some areas there has been a small increase of around 0.5oC per decade, to date. To most people 0.5-1oC does not seem a large increase and indeed, this change didn’t convince all those global warming skeptics who argued that ‘some places are in fact colder, some have only warmed a fraction and some have not warmed at all’.
As we have witnessed with many significant scientific discoveries/ theories in the past, the smallest hint of doubt can cause stark delays in acceptance on a large-scale. Many great discoveries have taken years to commonly be accepted and in some instances still aren’t accepted; for example the theory of Evolution. There are many reasons why a discovery/theory is not accepted, perhaps miscommunication, lack of understanding or that the discovery or theory conflicts with ideologies already established within communities and religions.
Warmer springs and milder winters are seen as natural changes. These changes have not been accepted as a synthetic result of burning fossil fuels to power industry and heat homes. However, with global weather patterns shifting and areas experiencing increased flooding, severe snow fall and tropical storms, it does offer the climate change theory some significant weight. People find it easier to accept what was once an abstract theory to them, when they can see it translated into reality, as it is in this case by extreme weather.
Greenhouse gases and examples from history
As I’m sure you are aware, carbon dioxide or CO2 are created as by combustion. The chemical formula is shown below. Carbon molecules use oxygen in the air to create carbon dioxide, water and energy.
2CH4 + 4O2 > 2CO2 + 2H2O + Energy
The product of this equation termed the Greenhouse Effect; combining the by-products and gases produced following combustion. In the atmosphere CO2 absorbs the sun’s energy and reflects it back to earth which keeps the energy within the atmosphere for longer periods. It is an essential process. Our current concentration, 0.03% of CO2, keeps the earth warm allowing for life on earth to evolve and prosper. If there are strong fluctuations of greenhouse gasses, like CO2 and methane, we can expect significant ramifications.
Looking back through the geological record we can see this has happened numerous times, most recently the Palaeocene Eocene thermal maximum (PETM). This is an important case study, documented in history approximately 56 million years ago. It parallels our current predicament; the earth was heating due to an increase in CO2 levels, believed to have come from severe episodes of volcanic activity, which created a positive carbon feedback loop. The feedback loop triggered the release of trapped methane gas, a stronger greenhouse gas which had the effect of accelerating the greenhouse effect causing significant extinction within the marine environment.
Methane gas is found frozen beneath the seabed, termed clathrates, and is locked away in a lattice structure, created by microbial breakdown of material below the seabed.
At the time the PETM had around 2 billion tons of carbon added each year to the atmosphere, all from natural sources such as volcanoes. Currently we are adding 30 billion tons each year, a staggering number. The only difference between then and now is the gradual transformation that allowed some species to adapt and cope with change, averting complete catastrophe. Now that this is occurring on such a rapid scale it is likely to prevent wildlife from adapting as they did 56 million years ago. WE have replaced the volcanism trigger in the PETM, so all that’s left is the methane outburst, which will have catastrophic consequences mainly because it doesn’t readily dissolve in water, therefore it will exasperate the greenhouse effect.
The impact of increasing sea temperatures on marine life is a complicated issue. In a normal climate regime CO2 dissolves in sea water (CO2 has polar bonds and attracts H2O) in equilibrium with air. The below formula shows this:
CO2 + H2O > H2CO3 Carbonic acid
H2CO3 > H+ + HCO3– Bicarbonate ion
HCO3– > H+ + CO32- Carbonate ion
These work in sequence and are reversible depending on the acidity, salinity and temperature of the air and sea. They are always in equilibrium, dissociating between the different states. It is important because the first state is an acid and the latter states are important for calcium carbonate generation for a multitude of wildlife. This simple mechanism is driving ocean change because of the outpouring of CO2 gas. More and more dissolves, which at first creates a surge in carbonate ions, but as the seas become slowly more acidic and the dynamic shifts to an aqueous form of CO2 thus an even lower pH.
These relationships that I have described above rely on a constant temperature, without warming, and a simple uptake of CO2 by the ocean. However gases dissolve less freely when the temperature increases, which leaves us with two distinct paradigms:
The Increased levels of CO2 dissolve in the ocean causing a decrease in pH resulting in less free carbonate ions. However, as the CO2 increases, the temperature rises and results in less gas dissolving. It should mean that there will be a tipping point where ocean acidification culminates at a certain temperature as the earth becomes warmer. A sudden global temperature spike will then follow, once no more is absorbed by the ocean (because it stays within the atmosphere) the greenhouse effect will then intensify.
The ocean does attempt to rectify this imbalance adjusting a natural feature, the carbonate compensation depth. This is an imaginary line which allows CaCO3 to precipitate out of solution and create layers like chalk and other calcareous rocks on the sea bed. It shoals rapidly to allow more precipitation of carbon from the water on the seabed and other rock structures. This happened to the PETM previously, but over a period of several thousand years. Obviously, if given time, the earth will eventually adjust the CO2 as you can in the below diagram the temperature begins to decrease.
The problem is that WE are causing rapid change. We will be long gone before the earth can sort out the mess that we continue to create.
Effects on marine life
This combined scenario is already taking place and will likely get worse. It is probable that all marine life will perish with increased temperature and acidification before we reach the tipping point and CO2 stops dissolving. The changing ocean chemistry disrupts all levels of the food chain related to this formula:
Ca2+ + 2HCO3– > CACO3 + CO2 + H2O
Calcium ions in this case combine with two bicarbonate ions creating calcium carbonate, carbon dioxide and water. This is what corals, coccolithophores, phytoplankton and many creatures at the bottom of the food chain need to grow. In normal situations creating CO2 would again dissociate to form bicarbonate ions fueling this equation again: A beautiful yet simple relationship that acts as a carbon sink, removing carbon from the atmosphere. If, however, the left part of the equation is more acidic than bicarbonate and preferentially becomes carbonic acid, nature cannot grow; the necessary reaction will be absent.
In initial studies it seems that molluscs and other animals grew much thinner and weaker outer shells with increased acidity and less bicarbonate concentration. This showed adults, but not the larval stages of growth that also need CACO3 to grow. This could suggest that many food chains will crash due to weakened growth and development at both the adult and adolescent stages.
At the bottom of the food web are the calcareous life forms, microscopic, which are essential for the food chain in the ocean. 2.4 kg of large fish such as tuna need around 1 tonne of phytoplankton within the food chain to grow. This means that fish stocks, for both the wildlife and humans that rely on fish as a food source, are dependent on the balancing of pH and carbonate in our oceans. How that balance effects the smallest creatures can cause severe ramifications from the bottom of the food chain all the way to the top.
What I’m hoping to express in this article is that acidification and climate change are certainly not trivial. Yes, there are impacts on weather systems which is seen across the world and hopefully this will help to force our hand towards change. But the oceans also share this ever increasing catastrophe, although it cannot be seen as tangibly as the weather!
There has been a change of pH from the 1700’s, to date, of approximately 8.16 to 8.05; this is a change of 0.11. Emissions are likely to increase this rate with estimations of a further 0.4 by the year 2100. At this point the pH will be below 8, as you can see from the graph above this puts 20% CO2 into aqueous form creating further acidity. This situation is likely to snowball.
We must act now
Currently, world leaders are attending talks in Paris, we hope that a positive outcome regarding a universal policy to combat climate change will be reached at these talks; for the sake of people suffering drought, famine or flooding as well as the changes to the oceans and wildlife. If they do not, we could be looking at one hell of a scary future.
The oceans gave us the oxygen we breathe and it will attempt to put things right, but we need to face up and help the ocean, as without us the ocean has no hope of stopping a repeat performance of what happened 56 million years ago!
Images adapted from Introducing Oceanography
Facts and details from http://www.wunderground.com/climate/PETM.asp?MR=1
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